Chlorination is known to improve the properties of certain resinous polymers, notably polyvinyl chloride, polyethylene, polypropylene and natural rubber.
Chlorinated polymers, e.g., chlorinated products of natural rubber, polyisoprene, polyethylene and polypropylene, are used as binders, e.g., for paints, adhesives and printing inks. Chlorinated polymers are usually prepared using gaseous chlorine or chlorinated hydrocarbons, such as carbon tetrachloride, trichloroethylene, chloroform or tetrachloroethane as solvents.
The chlorination of polyvinyl chloride (PVC) particles in an aqueous medium, using chlorine gas, is a three phase (Gas-Liquid-Solid) system. The surface chlorination of PVC particles occurs in the first phase, but the chlorination inside the pores of the PVC particles is also desirable for high chlorination yield as well as the uniformity in chlorination. Thus the diffusion of chlorine inside the pores of the polymer and penetration of radiation or light is essential. Though diffusion of chlorine gas occurs inside the pores, the penetration of light inside the pores is poor. The poor penetration of light inside the pores of PVC obstructs the formation of chlorine radicals. When the chlorine radicals are formed in the solution external to the particles, due to short life time the radical recombines with another radical by the time it diffuses inside the pores of the polymer.
Further, long exposure of radiation can degrade the polymer chain and thus it is recommended to have less exposure of radiation onto the polymer.
There is, therefore, felt a need to develop a process for the chlorination of polymers that obviates the drawbacks of the prior art.